There is a clear bias against chiropractic manipulation by most of mainstream medicine, but it is changing from public demand. There is a growing body of impressive evidence that it works for low back pain and for relieving headaches in people with cervical disc disease. In a meta-analysis of 9 studies, 6 showed a positive benefit from chiropractic. The dangers of cervical manipulation include the development of a stroke, but the literature shows that this is in the range of 3 per two million adjustments. There would be far more morbidity and mortality from just using NSAIDs, which are first line therapy in mainstream medical practice.
Fortunately, chiropractic is becoming more acceptable as patients are choosing it because it works! Many MDs are becoming more open minded about chiropractors and use chiropractic themselves.